<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    

    <script>
    var str = 'aabccd'
    var arr = str.split('')

    


    var res = arr.reduce(function(pre,cur){
        return pre.indexOf(cur) === -1? pre.concat(cur):pre
    },[])
    console.log(res);

    var res1 = res.join('')
    console.log(res1);
    
    
    </script>
    
</body>
</html>